1. Field of the Invention
The present invention relates to a safe utility knife. It can avoid the user to be injured accidentally. It can be operated by one hand to protrude the blade. This invention is suitable for regular blades available on the market. In addition, it can switch to the mode for manual automatic blade returning.
2. Description of the Prior Art
As shown in FIG. 13, it shows a traditional utility knife with automatic blade returning function. It includes a body 91, an engaging bar 92, a special blade 93, and a spring 94. The body 91 includes a body securing end 911, a pivoting part 912, a limit spring 913, a sliding rail 914, a front opening 915, and a rear opening 916. The engaging bar 92 has an engaging recess 921. This special blade 93 includes a blade portion 931, a pushing rod 932, a blade securing end 933, and an engaging protrusion 934. The engaging bar 92 has one end that is pivoted on the pivoting part 912 and is limited by the pushing force of the limit spring 913. The special blade 93 is able to slide on the sliding rail 914. This spring 94 has two ends that are disposed with the body securing end 911 and the blade securing end 933 respectively.
Therefore, by pushing the pushing rod 932 of the special blade 93, the engaging protrusion 934 and the engaging recess 921 are engaged together so as to make the blade portion 931 protruding from the front opening 915. As illustrated in FIG. 14, when a shaking, swaying, swinging or hitting force is generated by the user (who is holding it) and this force is larger than the pushing force of the limit spring 913, the engaging bar 92 will rotate up an angle so that it makes the engaging recess 921 separating from the engaging protrusion 934. Hence, the special blade 93 is pulled back by the limit spring 94. Accordingly, the special blade 93 moves back via this sliding rail 914.
However, about the traditional utility knife, it still has the following problems.
[1] It needs two hands to operate it. When the user wants to push the special blade 93 out, it needs one hand to hold one the body 91. Besides, it needs the other hand to push on the pushing rod 932 of the special blade 93. Thus, it is impossible to operate this action by one hand only.
[2] It is required the special blade. With regard to the traditional utility knife with automatic blade retuning function, only the special blade 93 can be used. Such special blade 93 is not a regular or common blade which is available on the market. It needs a special order (to manufacture it). Therefore, the cost for such special blade 93 is relative high.
[3] The special blade 93 is easy to break out. About the traditional utility knife with automatic blade returning function, the length of the pushing rod 932 of the special blade 93 is longer and the diameter of it is smaller. So, the special blade 93 is easy to be broken due to any hitting or dropping.
[4] Its safety is low. The traditional utility knife with automatic blade returning function has the disadvantage of easy breaking (about the special blade 93). If the special blade 93 is broken while the user is using it, it is possible to make the engaging protrusion 934 separating from the engaging recess 921. Then, the user might be injured.
[5] The automatic blade returning function is activated by gravity only. Concerning this traditional utility knife, the special blade 93 can be moved back by shaking, swaying, swinging or hitting method so as to force the special blade 93 back due to gravity. At this moment, the engaging protrusion 932 separates from the engaging recess 921, so as to achieve the automatic blade returning function.